In a fourth generation (4G) communication system, research has been conducted to provide users with various Quality of Service (QoS) levels at a data rate of about 100 Mbps. Specifically, research of 4G communication systems has been conducted into a high rate service support to guarantee mobility and QoS in Broadband Wireless Access (BWA) communication systems such as Local Area Network (LAN) systems and Metropolitan Area Network (MAN) systems. Representative 4G communication systems include Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication systems.
The 802.16 communication system defines modes of a terminal, which include a normal mode, a sleep mode, and an idle mode. In the normal mode, the terminal communicates with a base station. In the idle mode, the terminal returns a Connection ID (CID) and merely checks a periodic paging message. In the sleep mode, the terminal temporarily stops the communication without returning the CID.
To the terminal in the sleep mode, a frame includes a sleep interval and a listening interval by turns as shown in FIG. 1. The sleep interval and the listening interval are constituted on a frame basis. The sleep interval gradually increases from a minimum value to a maximum value, and the listening interval is a fixed value in the sleep mode. The sleeping terminal does not perform any operation at all in the sleep interval to save the power, and confirms a TRaFfic INDicator MeSsaGe (TRF-IND MSG) received from the base station in the listening interval. Herein, the TRF-IND MSG informs of whether there is traffic to be transmitted to the sleeping terminal. For doing so, the base station needs to schedule downlink resources to send the TRF-IND MSG in accordance with the listening interval.
To enter the sleep mode, the terminal requests a sleep mode entry to the base station. The base station determines whether to accept the sleep mode entry request by checking the number of the sleeping terminals at present. When the sleeping terminals admitted are not full, that is, when the number of the sleeping terminals at present does not reach a maximum value, the base station permits the sleep mode entry of the terminal.
As discussed above, by determining whether to enter the sleep mode solely based on the number of acceptable sleeping terminals, the sleep intervals and the listening intervals of the sleeping terminal are distributed irregularly. Thus, the base station has to separately manage the listening interval of each sleeping terminal on the terminal basis. In other words, since the listening intervals of the sleeping terminal are distributed irregularly, the scheduling of the base station for the sleeping terminal is seriously complicated.